1. Field of the Invention
The described embodiments relate generally to wireless communications. More particularly, the described embodiments relate to a method and system for selecting uplink sounding sub-carriers.
2. Background Art
Mobile WiMAX is a wireless platform being developed to provide wireless access that is able to deliver on demanding service requirements. With the added support for a variety of advanced multi-antenna implementations, Mobile WiMAX offers wireless access that meets growing network demands with higher performance, fewer sites, less spectrum, and reduced cost.
Multiple antenna techniques at the base station and end-user device, paired with sophisticated signal processing, can dramatically improve the communications link for the most demanding application scenarios including heavily obstructed propagation environments and high speed mobility service. Where conventional wireless network design has long used base site sectorization and single, omni-directional antennas at the end-user device to serve the communications link, with advanced multi-antenna implementations operators have a new techniques to develop the robust wireless networks.
Industry vendors and sources have created a host of naming conventions to refer to multi-antenna implementations. Simply put, the term MIMO (multiple input multiple output) can be used to reference any multi-antenna technologies. MIMO antenna systems are used in code division multiple access (CDMA) networks, time division multiplexing (TDM) networks, time division multiple access (TDMA) networks, orthogonal frequency division multiplexing (OFDM) networks, orthogonal frequency division multiple access (OFDMA) networks, and others. In order to maximize throughput, MIMO networks use a variety of channel estimation techniques to measure the transmission channel between a base stations of the wireless network and a mobile device. The channel estimation technique used depends on the wireless network type (i.e., CDMA, TDM/TDMA, OFDM/OFDMA).
Some methods of estimating the transmission channels rely on pilots that occupy valuable time and frequency transmission space. That is, the typical methods require dedicated signaling overhead which that requires bandwidth (time and/or frequency), and therefore, reduces system capacity.
Additionally, wireless networks that include mobile terminals (subscribers) have transmission channels that change frequently. Therefore, the transmission channels must be re-estimated or updated more frequently. As a result, wireless networks that include mobile terminals require even more capacity to be dedicated to channel estimations.
It is desirable to have a system and method for estimating and/or updating transmission channel information between a base station and a mobile terminal of a wireless network that reduces the amount of time and frequency channel capacity required for the uplink sounding pilots.